U.S. patent application number 10/560858 was filed with the patent office on 2006-09-07 for plasma generating electrode, plasma generation device, and exhaust gas purifying apparatus.
Invention is credited to Kenji Dosaka, Yasumasa Fujioka, Tatsuhiko Hatano, Yuuichiro Imanishi, Masaaki Masuda, Masanobu Miki, Yukio Miyairi, Takeshi Sakuma.
Application Number | 20060196762 10/560858 |
Document ID | / |
Family ID | 33534928 |
Filed Date | 2006-09-07 |
United States Patent
Application |
20060196762 |
Kind Code |
A1 |
Miki; Masanobu ; et
al. |
September 7, 2006 |
Plasma generating electrode, plasma generation device, and exhaust
gas purifying apparatus
Abstract
A plasma generating electrode 1 of the invention includes at
least a pair of electrodes 5, at least one electrode 5a of the pair
of electrodes 5 including a plate-like ceramic body 2 as a
dielectric and a plurality of conductive films 3 disposed in the
ceramic body 2 and each having a plurality of through-holes 4
formed through the conductive film 3 in its thickness direction in
a predetermined arrangement pattern, the through-holes 4 having a
cross-sectional shape including an arc shape along a plane
perpendicular to the thickness direction, an arrangement pattern of
the through-holes 4a formed in at least one conductive film 3a
being different from an arrangement pattern of the through-holes 4b
formed in the other conductive film 3b. The plasma generating
electrode 1 is capable of simultaneously generating different
states of plasma upon application of voltage between the pair of
electrodes 5 due to the different arrangement patterns of the
through-holes 4 in the conductive films 3.
Inventors: |
Miki; Masanobu;
(Saitama-ken, JP) ; Dosaka; Kenji; (Saitama-ken,
JP) ; Miyairi; Yukio; (Aichi-prefecture, JP) ;
Fujioka; Yasumasa; (Aichi-prefecture, JP) ; Masuda;
Masaaki; (Aichi-prefecture, JP) ; Hatano;
Tatsuhiko; (Aichi-prefecture, JP) ; Sakuma;
Takeshi; (Aichi-prefecture, JP) ; Imanishi;
Yuuichiro; (Aichi-prefecture, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Family ID: |
33534928 |
Appl. No.: |
10/560858 |
Filed: |
June 18, 2004 |
PCT Filed: |
June 18, 2004 |
PCT NO: |
PCT/JP04/08618 |
371 Date: |
December 15, 2005 |
Current U.S.
Class: |
204/157.3 |
Current CPC
Class: |
Y02C 20/30 20130101;
F01N 13/009 20140601; F01N 2240/28 20130101; H05H 1/2418 20210501;
H05H 1/2406 20130101; H01J 37/3244 20130101; F01N 3/0892 20130101;
H01J 37/32844 20130101 |
Class at
Publication: |
204/157.3 |
International
Class: |
B01D 53/00 20060101
B01D053/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 20, 2003 |
JP |
2003-177233 |
Claims
1. A plasma generating electrode comprising at least a pair of
electrodes disposed opposite to each other and capable of
generating plasma upon application of voltage between the
electrodes, at least one of the pair of electrodes including a
plate-like ceramic body as a dielectric and a plurality of
conductive films disposed inside the ceramic body without
overlapping with one another and each having a plurality of
through-holes formed through the conductive film in its thickness
direction in a predetermined arrangement pattern, the through-holes
having a cross-sectional shape including an arc shape along a plane
perpendicular to the thickness direction, an arrangement pattern of
the through-holes formed in at least one of the conductive films
being different from the arrangement pattern of the through-holes
formed in the other conductive film, the plasma generating
electrode being capable of simultaneously generating different
states of plasma upon application of voltage between the pair of
electrodes due to the different arrangement patterns of the
through-holes in the conductive films.
2. A plasma generating electrode comprising at least a pair of
electrodes disposed opposite to each other and generating plasma
upon application of voltage between the electrodes, at least one of
the pair of electrodes including a plate-like ceramic body as a
dielectric and at least one conductive film disposed inside the
ceramic body and having a plurality of through-holes formed through
the conductive film in its thickness direction in two or more
different arrangement patterns, the through-holes having a
cross-sectional shape including an arc shape along a plane
perpendicular to the thickness direction, the plasma generating
electrode being capable of simultaneously generating different
states of plasma upon application of voltage between the pair of
electrodes due to the different arrangement patterns of the
through-holes in the conductive film.
3. The plasma generating electrode according to claim 1, wherein
the through-holes have a circular cross-sectional shape along a
plane perpendicular to the thickness direction.
4. The plasma generating electrode according to claim 1, wherein at
least one of the conductive films includes a metal differing from
that of the other conductive film as a major component.
5. The plasma generating electrode according to claim 1, wherein
the conductive film includes at least one metal selected from the
group consisting of tungsten, molybdenum, manganese, chromium,
titanium, zirconium, nickel, iron, silver, copper, platinum, and
palladium as a major component.
6. The plasma generating electrode according to claim 1, wherein
the conductive film is disposed inside the ceramic body by screen
printing, calender rolling, spraying, chemical vapor deposition, or
physical vapor deposition.
7. A plasma generation device comprising the plasma generating
electrode according to claim 1.
8. An exhaust gas purifying device comprising the plasma generation
device according to claim 7 and a catalyst, the plasma generation
device and the catalyst being disposed in an exhaust system of an
internal combustion engine.
Description
TECHNICAL FIELD
[0001] The present invention relates to a plasma generating
electrode, a plasma generation device, and an exhaust gas purifying
device. More particularly, the present invention relates to a
plasma generating electrode and a plasma generation device capable
of simultaneously generating different states of plasma. The
present invention also relates to an exhaust gas purifying device
capable of purifying exhaust gas well.
BACKGROUND ART
[0002] It is known that silent discharge occurs when disposing a
dielectric between two electrodes and applying a high alternating
current voltage or a periodic pulsed voltage between the
electrodes. In the resulting plasma field, active species,
radicals, and ions are produced to promote reaction and
decomposition of gas. This phenomenon may be utilized to remove
toxic components contained in engine exhaust gas or incinerator
exhaust gas.
[0003] For example, a plasma exhaust gas treatment system has been
disclosed in which NO.sub.x, carbon particulate, HC, and CO
contained in engine exhaust gas or incinerator exhaust gas is
oxidized by causing the engine exhaust gas or incinerator exhaust
gas to pass through plasma (e.g. JP-A-2001-164925).
DISCLOSURE OF THE INVENTION
[0004] However, since exhaust gas contains a plurality of
substances and intensity of plasma suitable for treatment differs
for each substance, a plasma generating electrode designed to treat
a predetermined substance cannot be used to treat another
substance. This makes it necessary to provide a plurality of plasma
generating electrodes when treating exhaust gas containing a
plurality of substances. Moreover, since high-intensity plasma must
be generated in the case of treating a plurality of substances by
using one kind of plasma, power consumption is increased. A
NO.sub.x reduction catalyst used for an exhaust gas purifying
device such as an SCR device, which further treats a gas passed
through the plasma generating electrode, reduces nitrogen dioxide
(NO.sub.2) into oxygen and nitrogen by using a fuel (hydrocarbon)
contained in exhaust gas. However, since hydrocarbons are oxidized
by high-intensity plasma, the performance of the NO.sub.x reduction
catalyst is decreased.
[0005] The present invention has been achieved in view of the
above-described problems and provides a plasma generating electrode
and a plasma generation device capable of simultaneously generating
different states of plasma. The present invention also provides an
exhaust gas purifying device which includes the above plasma
generation device and a catalyst and can purify exhaust gas
well.
[0006] In order to achieve the above objects, the present invention
provides the following plasma generating electrode, plasma
generation device, and exhaust gas purifying device.
[0007] [1] A plasma generating electrode comprising at least a pair
of electrodes disposed opposite to each other and capable of
generating plasma upon application of voltage between the
electrodes, at least one of the pair of electrodes including a
plate-like ceramic body as a dielectric and a plurality of
conductive films disposed inside the ceramic body without
overlapping with one another and each having a plurality of
through-holes formed through the conductive film in its thickness
direction in predetermined arrangement patterns, the through-holes
having a cross-sectional shape including an arc shape along a plane
perpendicular to the thickness direction, an arrangement pattern of
the through-holes formed in at least one of the conductive films
being different from an arrangement pattern of the through-holes
formed in the other conductive film, the plasma generating
electrode being capable of simultaneously generating different
states of plasma upon application of voltage between the pair of
electrodes due to the different arrangement patterns of the
through-holes in the conductive films (hereinafter may be called
"first invention").
[0008] [2] A plasma generating electrode comprising at least a pair
of electrodes disposed opposite to each other and generating plasma
upon application of voltage between the electrodes, at least one of
the pair of electrodes including a plate-like ceramic body as a
dielectric and at least one conductive film disposed inside the
ceramic body and having a plurality of through-holes formed through
the conductive film in its thickness direction in two or more
different arrangement patterns, the through-holes having a
cross-sectional shape including an arc shape along a plane
perpendicular to the thickness direction, the plasma generating
electrode being capable of simultaneously generating different
states of plasma upon application of voltage between the pair of
electrodes due to the different arrangement patterns of the
through-holes in the conductive film (hereinafter may be called
"second invention").
[0009] [3] The plasma generating electrode according to [1] or [2],
wherein the through-holes have a circular cross-sectional shape
along a plane perpendicular to the thickness direction.
[0010] [4] The plasma generating electrode according to any of [1]
to [3], wherein at least one of the conductive films includes a
metal differing from that of the other conductive film as a major
component.
[0011] [5] The plasma generating electrode according to any of [1]
to [4], wherein the conductive film includes at least one metal
selected from the group consisting of tungsten, molybdenum,
manganese, chromium, titanium, zirconium, nickel, iron, silver,
copper, platinum, and palladium as a major component.
[0012] [6] The plasma generating electrode according to any of [1]
to [5], wherein the conductive film is disposed inside the ceramic
body by screen printing, calender rolling, spraying, chemical vapor
deposition, or physical vapor deposition.
[0013] [7] A plasma generation device comprising the plasma
generating electrode according to any of [1] to [6] (hereinafter
may be called "third invention").
[0014] [8] An exhaust gas purifying device comprising the plasma
generation device according to [7] and a catalyst, the plasma
generation device and the catalyst being disposed in an exhaust
system of an internal combustion engine (hereinafter may be called
"fourth invention").
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] [FIG. 1] FIG. 1 is an oblique diagram schematically showing
one embodiment of a plasma generating electrode of the present
invention (first invention).
[0016] [FIG. 2] FIG. 2 is a plan view schematically showing an
example of a ceramic body and a conductive film constituting an
electrode in one embodiment of the plasma generating electrode of
the present invention (first invention).
[0017] [FIG. 3] FIG. 3 is a perspective view schematically showing
another embodiment of the plasma generating electrode of the
present invention (first invention).
[0018] [FIG. 4] FIG. 4 is a plan view schematically showing another
example of a ceramic body and a conductive film constituting one
electrode in one embodiment of the plasma generating electrode of
the present invention (first invention).
[0019] [FIG. 5] FIG. 5 is a plan view schematically showing another
example of a ceramic body and a conductive film constituting one
electrode in one embodiment of the plasma generating electrode of
the present invention (first invention).
[0020] [FIG. 6] FIG. 6 is a plan view schematically showing another
example of a ceramic body and a conductive film constituting one
electrode in one embodiment of the plasma generating electrode of
the present invention (first invention).
[0021] [FIG. 7] FIG. 7 is a plan view schematically showing another
example of a ceramic body and a conductive film constituting one
electrode in one embodiment of the plasma generating electrode of
the present invention (first invention).
[0022] [FIG. 8] FIG. 8 is a plan view schematically showing another
example of the ceramic body and a conductive film constituting one
electrode in one embodiment of the plasma generating electrode of
the present invention (first invention).
[0023] [FIG. 9] FIG. 9 is a perspective view schematically showing
one embodiment of a plasma generating electrode of the present
invention (second invention).
[0024] [FIG. 10] FIG. 10 is a plan view schematically showing an
example of a ceramic body and a conductive film constituting one
electrode in one embodiment of the plasma generating electrode of
the present invention (second invention).
[0025] [FIG. 11(a)] FIG. 11(a) is a cross-sectional view showing
one embodiment of a plasma generation device of the present
invention (third invention) along a plane including the treatment
target fluid flow direction.
[0026] [FIG. 11(b)] FIG. 11(b) is a cross-sectional view along the
line A-A shown in FIG. 11(a).
[0027] [FIG. 12] FIG. 12 is an explanatory view schematically
showing one embodiment of an exhaust gas purifying device of the
invention (fourth invention).
BEST MODE FOR CARRYING OUT THE INVENTION
[0028] Embodiments of a plasma generating electrode, a plasma
generation device, and an exhaust gas purifying device of the
present invention are described below in detail with reference to
the drawings.
[0029] FIG. 1 is a perspective view schematically showing one
embodiment of a plasma generating electrode of the present
invention (first invention), and FIG. 2 is a plan view
schematically showing a ceramic body and a conductive film
constituting one electrode of the plasma generating electrode. As
shown in FIGS. 1 and 2, a plasma generating electrode 1 of the
present embodiment includes at least a pair of electrodes 5
disposed opposite to each other and can generate plasma upon
application of voltage between the electrodes 5, at least one
electrode 5a of the pair of electrodes 5 including a plate-like
ceramic body 2 as a dielectric and a plurality of conductive films
3 disposed inside the ceramic body 2 and each having a plurality of
through-holes 4 formed through the conductive film 3 in its
thickness direction in a predetermined arrangement pattern, the
through-holes having a cross-sectional shape including an arc shape
along a plane perpendicular to the thickness direction, an
arrangement pattern of the through-holes 4a formed in at least one
conductive film 3a being different from an arrangement pattern of
the through-holes 4b formed in another conductive film 3b, the
plasma generating electrode 1 being capable of simultaneously
generating different states of plasma upon application of voltage
between the pair of electrodes 5 due to the different arrangement
patterns of the through-holes 4 in the conductive films 3. In the
present embodiment, the configuration of the other electrode 5b is
not particularly limited, and known metal electrode may be used as
shown in FIG. 1. As shown in FIG. 3, it is preferable that the
other electrode 5b of the plasma generating electrode 1 include a
plurality of conductive films each having a plurality of
through-holes formed in an arrangement pattern different from those
of the other conductive films in the same manner as the electrode
5a. In this case, it is preferable that connection sections for
respectively supplying current to the electrode 5a and the
electrodes 5b be formed in opposite directions.
[0030] In the plasma generating electrode 1 shown in FIG. 1, two
electrodes 5 are disposed opposite to each other. However, the
number of electrodes 5 is not limited to two. For example, three or
more electrodes may be disposed in parallel so that adjacent
electrodes respectively form a pair of electrodes (not shown).
[0031] FIGS. 1 and 2 illustrate the through-holes 4 having a
circular cross-sectional shape along a plane perpendicular to the
thickness direction. However, the cross-sectional shape of the
through-holes 4 is not limited to circular and may be a shape
including an arc shape such as an ellipse or a polygon having round
vertices, for example.
[0032] The plasma generating electrode 1 of the present embodiment
is a barrier discharge type electrode 5 including the plate-like
ceramic body 2 as a dielectric and the conductive films 3 disposed
inside the ceramic body 2 without overlapping with one another. The
plasma generating electrode 1 may suitably be used for an exhaust
gas treatment device or an exhaust gas purifying device which
treats treatment target fluid such as exhaust gas by passing the
treatment target fluid through plasma generated between the pair of
electrodes 5 or an ozonizer which produces ozone by reacting oxygen
contained in air, for example.
[0033] Since the through-holes 4 forming each arrangement pattern
have a shape including an arc shape, discharge uniformly occurs at
the outer periphery of the through-holes 4 as discharge starting
points. Moreover, since the through-holes 4 are formed over the
entire area of each conductive film 3 in a predetermined
arrangement pattern, stable and uniform plasma can be generated
over the entire electrode 5. If the shape of the through-hole 4 is
not circular and is polygonal or the like, discharge is
concentrated at locations corresponding to the vertices of the
polygon so that uniform plasma cannot be generated.
[0034] The principle of printing different states of plasma
simultaneously in the plasma generating electrode 1 of the present
embodiment is briefly described below. The capacitance of the
conductive film 3a and the capacitance of the conductive film 3b
can be made different by forming an arrangement pattern of the
through-holes 4a formed in the conductive film 3a in such a manner
that it differ from an arrangement pattern of the through-holes 4b
formed in the conductive film 3b. Different states of discharge
occur between the conductive films 3a and 3b due to the difference
in capacitance, so that different states of plasma can be
generated. Making arrangement patterns differ between the
conductive films 3 sometimes makes length of the outer periphery of
the through-hole 4 per unit area differs between the conductive
films 3. This also causes different discharge to occur in the
conductive films 3.
[0035] In the present embodiment, it is preferable that an
arrangement pattern of the through-holes 4 formed in each
conductive film 3 be configured so that plasma at predetermined
intensity can be generated. The intensity of plasma generated
between the electrodes 5 is determined depending on the material
and the capacitance of the conductive film 3, voltage applied to
the electrode 5, distance between the electrodes 5a and 5b, and the
like. The intensity of plasma generated on each conductive film 3
can be adjusted by causing different capacitance among the
conductive films 3 by utilizing the arrangement patterns of the
through-holes 4.
[0036] In the present embodiment, at least one conductive film 3a
may include metal differing from that of the conductive film 3b as
the major component. This enables the capacitance of the conductive
film 3a and the conductive film 3b to be adjusted by utilizing the
material, so that plasma at desired intensity can easily be
generated by the conductive films 3a and 3b.
[0037] In the plasma generating electrode 1 of the present
embodiment, electricity may be supplied to the conductive film 3a
and the conductive film 3b from either a single power source or
different power sources.
[0038] In FIG. 2, the electrode 5a includes two conductive films 3a
and 3b and the through-holes 4a and 4b having different diameters
are formed at different intervals. However, the arrangement
patterns of the through-holes 4a and 4b are not limited thereto. As
shown in FIG. 4, the through-holes 4a and 4b may have the same
diameter, and different arrangement patterns may be formed by
changing the intervals of the through-holes 4a and 4b. The
arrangement positions, size, and number of the conductive films 3a
and 3b are not particularly limited. As shown in FIGS. 5 to 8,
through-holes 4c, 4d, and 4e may be respectively formed in
conductive films 3c, 3d, and 3e at predetermined arrangement
patterns, for example.
[0039] As described above, since the plasma generating electrode 1
of the present embodiment can simultaneously generate different
states of plasma between a pair of electrodes 5, at the time of
treating (purifying) exhaust gas discharged from an internal
combustion engine such as an automotive engine, soot can be
oxidized by plasma generated by the conductive film 3a, and
nitrogen monoxide (NO) can be oxidized by plasma generated by the
conductive film 3b.
[0040] The arrangement method for a pair of electrodes and an
exhaust gas treatment process at the time of using the plasma
generating electrode 1 of the present embodiment for an exhaust gas
treatment device or an exhaust gas purifying device are described
below. In the case of using the plasma generating electrode
including the electrode 5a shown in FIGS. 2 and 4 for an exhaust
gas treatment device and passing exhaust gas through the exhaust
gas treatment device in the direction indicated by the arrow A, the
exhaust gas can continuously be passed through different states of
plasma generated by the conductive films 3a and 3b, so that a
plurality of substances contained in the exhaust gas can
effectively be treated. The electrode 5a shown in FIGS. 5 to 8 is
configured to be suitably used to treat exhaust gas containing
soot. In more detail, in the case of using the plasma generating
electrode including the electrode 5a shown in FIGS. 5 and 6, plasma
having high oxidizing properties capable effectively oxidizing soot
is generated by the conductive film 3d, and plasma having low
oxidizing properties for oxidizing a substance which is relatively
easily oxidized, such as NO or CO, is generated by the conductive
film 3e, for example. In the case of passing exhaust gas over the
electrode 5a in the direction indicated by the arrow A, soot having
a relatively large mass among the treatment target substances is
drawn by plasma generated by the conductive film 3c to form a
partial flow of soot in the exhaust gas flow. Soot is then oxidized
by plasma generated by the conductive film 3d, and NO, CO, and the
like are oxidized by plasma generated by either the conductive film
3d or the conductive film 3e. Since a region constituted by only
plasma exhibiting low oxidizing properties can be formed between
the pair of electrodes 5 (see FIG. 1) in the direction parallel to
the exhaust gas flow direction by this constitution, the exhaust
gas can be discharged in a state in which fuel (hydrocarbon)
contained in the exhaust gas is not completely oxidized, that is,
in a state in which the hydrocarbon is converted into aldehyde or
the like. Therefore, in the case of treating exhaust gas in
combination with an NO.sub.x reduction catalyst or the like, the
efficiency can be improved.
[0041] In the case of using the plasma generating electrode
including the electrode 5a shown in FIGS. 7 and 8, a circular flow
of exhaust gas is caused before passing the exhaust gas through
plasma, and a partial flow of soot is formed in the exhaust gas
flow by centrifugal force. Plasma exhibiting high oxidizing
properties is generated in the region (i.e. conductive film 3c) in
which the exhaust gas having the partial flow of soot passes, and
plasma exhibiting low oxidizing properties is generated in another
region (i.e. conductive film 3d), so that an effect similar to that
of the case of using the electrode 5a shown in FIGS. 5 and 6 can be
obtained.
[0042] It is preferable that the conductive film 3 used in the
present embodiment have a thickness corresponding to 0.1 to 10% of
the thickness of the ceramic body 2. This enables uniform discharge
to occur on a surface of the ceramic body 2 as a dielectric. The
thickness of the conductive film 3 is preferably about 5 to 50
.mu.m in order to reduce the size of the plasma generating
electrode 1 and reduce the resistance of the treatment target fluid
such as exhaust gas which is passed through the space between the
pair of electrodes 5. If the thickness of the conductive film 3 is
less than 5 .mu.m, reliability may be decreased in the case of
forming the conductive film 3 by printing or the like. Moreover,
since the resistance of the resulting conductive film 3 may be
increased, the plasma generation efficiency may be decreased. If
the thickness of the conductive film 3 is more than 50 .mu.m, the
resistance of the conductive film 3 is reduced. However, since the
conductive film 3 having such a thickness may affect the uniformity
of the surface of the ceramic body 2, it may be necessary to
process the surface of the ceramic body 2 so that the surface
becomes flat.
[0043] In the present embodiment of the invention, it is preferable
that the conductive film 3 forming the electrode 5a be disposed
inside the ceramic body 2 so that the conductive film 3 is
positioned at approximately an equal distance from both the
surfaces of the ceramic body 2. This enables plasma at equal
intensity to be generated between the adjacent electrodes, even in
the case of generating plasma in a state in which a plurality of
electrodes are continuously disposed opposite to one another. When
the conductive film 3 is disposed so that the conductive film 3 is
positioned at different distances from both the surfaces of the
ceramic body 2, the capacitance differs between the surfaces of the
electrode 5a, so that the discharge characteristics may differ
between the surfaces of the electrode 5a.
[0044] The conductive film 3 used in the present embodiment
preferably includes metal exhibiting excellent conductivity as the
major component. As preferable examples of the major component of
the conductive film 3, at least one kind of metal selected from the
group consisting of tungsten, molybdenum, manganese, chromium,
titanium, zirconium, nickel, iron, silver, copper, platinum, and
palladium can be given. In the present embodiment, the term "major
component" refers to a component accounting for 60 mass % or more
of the components of the conductive film 3. When the conductive
film 3 contains two or more kinds of metals selected from the
above-mentioned group as the major component, the total amount of
the metal accounts for 60 mass % or more of the components of the
conductive film 3.
[0045] As an example of a method of disposing the conductive film 3
inside the ceramic body 2, a method of embedding the conductive
film 3, such as a metal plate or metal foil, in a press-formed body
obtained by powder-pressing can be given. In more detail, at the
time of forming a press-formed body (ceramic body) by
powder-pressing, a metal plate or metal foil containing the
above-mentioned metal as the major component is embedded so that
the metal plate or metal foil is positioned at an equal distance
(distance in the thickness direction) from both the surfaces of the
press-formed body. Since the embedded metal foil or the like may be
deformed or cut due to sintering shrinkage of the ceramics, it is
preferable to sinter the press-formed body so that mass transfer is
suppressed in the horizontal (planar) direction. By this
constitutions, the press-formed body may be sintered while applying
pressure to the press-formed body in its thickness direction.
[0046] The conductive film 3 may be applied to the ceramic body 2.
As suitable examples of the application method, screen printing,
calender rolling, dip coating, chemical vapor deposition, and
physical vapor deposition, can be given. According to these
methods, the conductive film 3 exhibiting excellent surface
flatness and smoothness after application and having a small
thickness can easily be formed. Among the above-mentioned methods,
chemical vapor deposition and physical vapor deposition may
increase cost. However, these methods enable a thinner conductive
film to be easily disposed and through-holes having a smaller
diameter and a smaller center-to-center distance to be easily
formed.
[0047] At the time of applying the conductive film 3 to the ceramic
body 2, powder of the metal mentioned above as the major component
of the conductive film 3, an organic binder, and a solvent such as
terpineol may be mixed together to form a conductive paste, and the
conductive paste may be applied to the ceramic body 2 by using the
above-mentioned method. An additive may optionally be added to the
conductive paste in order to improve adhesion to the ceramic body 2
and improve sinterability.
[0048] The adhesion between the conductive film 3 and the ceramic
body 2 can be improved by adding the same component as the
component of the ceramic body 2 to the metal component of the
conductive film 3. A glass component may be added to the ceramic
component added to the metal component. The addition of the glass
component improves the sinterability of the conductive film 3 so
that the density of the conductive film 3 is improved in addition
to adhesion. The total amount of the component of the ceramic body
2 and/or the glass component other than the metal component is
preferably 30 mass % or less. If the total amount exceeds 30 mass
%, the function of the conductive film 3 may not obtained due to
decrease in resistance.
[0049] The ceramic body 2 of the present embodiment has a function
as a dielectric as described above. By using the conductive film 3
in a state in which the conductive film 3 is held inside the
ceramic body 2, local discharge such as a spark is reduced and
small discharge can be caused at multiple locations in comparison
with the case of causing discharge by using the conductive film 3
alone. Since such small discharge causes a small amount of current
to flow in comparison with discharge such as a spark, power
consumption can be reduced. Moreover, a current which flows between
the electrodes 5 is limited due to the presence of the dielectric,
so that non-thermal plasma which does not cause a rise in
temperature and consumes only a small amount of energy can be
generated.
[0050] The ceramic body 2 used in the present embodiment preferably
includes a material having a high dielectric constant as the major
component. As the material for the ceramic body 2, aluminum oxide,
zirconium oxide, silicon oxide, titanium-barium type oxide,
magnesium-calcium-titanium type oxide, barium-titanium-zinc type
oxide, silicon nitride, aluminum nitride, or the like may suitably
be used. The plasma generating electrode 1 can be operated at high
temperature by using a material exhibiting excellent thermal shock
resistance as the major component of the ceramic body 2.
[0051] The thickness of the ceramic body 2 is preferably 0.1 to 3
mm, although the thickness of the ceramic body 2 is not
particularly limited. If the thickness of the ceramic body 2 is
less than 0.1 mm, it may be difficult to ensure electric insulating
properties of the electrode 5. If the thickness of the ceramic body
2 is more than 3 mm, reduction in size of an exhaust gas purifying
system may be hindered. Moreover, the applied voltage must be
increased due to an increase in the electrode-to-electrode
distance, whereby the efficiency may be decreased.
[0052] As the ceramic body 2 used in the embodiment, a ceramic
green sheet for a ceramic substrate may suitably be used. The
ceramic green sheet may be obtained by forming slurry or paste for
a green sheet to have a predetermined thickness by using a
conventionally known method such as a doctor blade method, a
calender method, a printing method, or a reverse roll coating
method. The resulting ceramic green sheet may be subjected to
cutting, grinding, punching, or formation of communicating opening,
or may be used as an integral laminate in which the green sheets
are layered and bonded by thermocompression bonding or the
like.
[0053] As slurry or paste for a green sheet, a mixture prepared by
mixing an appropriate binder, sintering agent, plasticizer,
dispersant, organic solvent, and the like into a predetermined
ceramic powder may suitably be used. As suitable examples of the
ceramic powder, alumina, mullite, ceramic glass, zirconia,
cordierite, silicon nitride, aluminum nitride, and glass can be
given. As suitable examples of the sintering agent, silicon oxide,
magnesium oxide, calcium oxide, titanium oxide, and zirconium oxide
can be given. The sintering agent is preferably added in an amount
of 3 to 10 parts by mass for 100 parts by mass of the ceramic
powder. As the plasticizer, dispersant, and organic solvent, those
used for a conventionally known method may suitably be used.
[0054] As the ceramic body 2 used in the present embodiment, a
ceramic sheet formed by extrusion may also suitably be used. For
example, a plate-like ceramic formed body obtained by extruding a
mixture prepared by mixing the above-mentioned ceramic powder with
a forming agent such as methyl cellulose, a surfactant, and the
like through a predetermined die may be used.
[0055] In the present embodiment, the porosity of the ceramic
formed body 2 is preferably 0.1 to 35%, and more preferably 0.1 to
10%. This allows plasma to be efficiently generated between the
electrode 5a including the ceramic body 2 and the electrode 5b
disposed opposite to the electrode 5a, so that energy saving can be
realized.
[0056] It is preferable that the pair of electrodes 5 be disposed
at such a distance that plasma can effectively be generated
therebetween. The electrodes 5 are preferably disposed at a
distance of 0.1 to 5 mm although the distance may differ depending
on the voltage applied to the electrodes or the like.
[0057] A method of manufacturing the plasma generating electrode of
the present embodiment is described below in detail.
[0058] First, a ceramic green sheet used as the above ceramic body
is provided. For example, the aforementioned sintering agent, a
binder such as a butyral resin or a cellulose resin, a plasticizer
such as DOP or DBP, an organic solvent such as toluene or
butadiene, and the like are added to at least one kind of material
selected from the group consisting of alumina, mullite, ceramic
glass, and glass. The components are sufficiently mixed by using an
alumina pot and an alumina ball to prepare a green sheet slurry. A
green sheet slurry may be prepared by mixing the materials by ball
milling using a mono ball.
[0059] The resulting green sheet slurry is stirred under reduced
pressure for degassing and adjusted to have a predetermined
viscosity. The green sheet slurry is formed in the shape of a tape
by using a tape forming method such as a doctor blade method to
form an unfired ceramic body.
[0060] A conductive paste for forming a conductive film disposed on
one surface of the unfired ceramic body is provided. The conductive
paste may be prepared by adding a binder and a solvent such as
terpineol to silver powder and sufficiently kneading the mixture by
using a triroll mill, for example.
[0061] The resulting conductive paste is printed on a surface of
the unfired ceramic body by screen printing or the like to form
conductive films. At this time, the conductive paste is printed so
that through-holes are formed in the conductive films in different
arrangement patterns. In order to supply electricity to the
conductive films from the outside after holding the conductive
films inside the unfired ceramic body, the conductive paste is
preferably printed so that each conductive film extends to the
outer periphery of the unfired ceramic body.
[0062] At the time of forming the conductive films by printing the
conductive paste, the conductive films having different
through-hole arrangement patterns may be formed by either
simultaneously or separately printing the conductive paste.
Different types of conductive paste may be printed so that the
conductive films contain different major components.
[0063] Another unfired ceramic formed body is layered on the
unfired ceramic body on which the conductive films are printed so
that the printed conductive films are covered. The unfired ceramic
formed bodies are preferably layered at a temperature of
100.degree. C. while applying a pressure of 10 MPa.
[0064] Then, the resulting laminate is fired to form an electrode
including a plate-like ceramic body as a dielectric and conductive
films disposed inside the ceramic body without overlapping with one
another.
[0065] An electrode as a counter electrode is disposed opposite to
the resulting electrode to form a plasma generating electrode of
the present embodiment. As the electrode used as the counter
electrode, an electrode obtained by using the above-described
manufacturing method or an electrode having a conventionally known
configuration may be used.
[0066] One embodiment of a plasma generating electrode of the
present invention (second invention) is described below. As shown
in FIGS. 9 and 10, a plasma generating electrode 21 of the present
embodiment includes at least a pair of electrodes 25 disposed
opposite to each other and generates plasma upon application of
voltage between the electrodes 25, at least one electrode 25a of
the pair of electrodes 25 including a plate-like ceramic body 22 as
a dielectric and a conductive film 23 disposed inside the ceramic
body 22 and having a plurality of through-holes 24 formed through
the conductive film 23 in its thickness direction in two or more
different arrangement patterns, the through-holes 24 having a
cross-sectional shape including an arc shape along a plane
perpendicular to the thickness direction, the plasma generating
electrode 21 being capable of simultaneously generating different
states of plasma upon application of voltage between the pair of
electrodes 25 due to the different arrangement patterns of the
through-holes 24a and 24b in the conductive film 23.
[0067] In the plasma generating electrode 21 of the present
embodiment, the through-holes 24a and 24b are formed in one
conductive film 23 in two or more different arrangement patterns,
differing from the first invention in which one electrode includes
a plurality of conductive films. The configuration in which the
through-holes 24a and 24b are formed in different arrangement
patterns allows different discharge to occur due to the different
arrangement patterns, so that different states of plasma can be
generated.
[0068] Since the plasma generating electrode 21 of the present
embodiment can simultaneously generate different states of plasma
between the electrodes 25, at the time of treating exhaust gas
discharged from an automotive engine, soot can be oxidized by
plasma generated in the region in which the through-holes 24a are
formed in one arrangement pattern, and nitrogen oxide (e.g. NO) can
be oxidized by plasma generated in the region in which the
through-holes 24b are formed in another arrangement pattern.
Therefore, an effect similar to that of the plasma generating
electrode of the first invention can be obtained.
[0069] As the conductive film 23 constituting the plasma generating
electrode 21 of the present embodiment, a conductive film
configured in the same manner as the conductive film described in
to one embodiment of the first invention may suitably be used,
except that the through-holes 24a and 24b formed through the
thickness direction of the conductive film 23 and having a
cross-sectional shape including an arc shape along a plane
perpendicular to the thickness direction are formed in two or more
different arrangement patterns. FIGS. 9 and 10 illustrate the
through-holes 24a and 24b having a circular cross-sectional shape
along a plane perpendicular to the thickness direction. However,
the cross-sectional shape of the through-holes 24a and 24b is not
limited to a circle, but may be an ellipse, a shape in which a
polygon has the rounded vertice, or the like. The conductive film
23 may be formed by using a method similar to the method described
in one embodiment of the first invention except for forming the
through-holes 24a and 24b in two or more different arrangement
patterns. As the ceramic body 22 constituting the plasma generating
electrode 21 of the present embodiment, a ceramic body configured
in the same manner as the ceramic body described in one embodiment
of the first invention may suitably be used.
[0070] FIG. 10 shows two arrangement patterns in which the
through-holes 24a and 24b having different diameters are arranged
at different intervals. However, the arrangement patterns of the
through-holes 24a and 24b are not limited thereto. The arrangement
patterns may be made different by disposing the through-holes 24a
and 24b having the same diameter at different intervals (not
shown). The number of arrangement patterns is not limited to two as
long as it is two or more.
[0071] One embodiment of a plasma generation device of the present
invention (third invention) is described below. As shown in FIGS.
11(a) and 11(b), a plasma generation device 10 of the present
embodiment includes the plasma generating electrode 1 according to
the first or second invention. In more detail, the plasma
generation device 10 of the present embodiment includes a plasma
generating electrode 31 and a casing 11 which accommodates a pair
of electrodes 35 constituting the plasma generating electrode 10 in
a state in which a treatment target fluid such as exhaust gas can
pass through the space between a pair of electrodes 35. The casing
11 includes an inlet port 12 through which the treatment target
fluid flows, and an outlet port 13 through which the treated fluid
obtained by treating the treatment target fluid by passing the
fluid through the space between the electrodes 35 is
discharged.
[0072] Since the plasma generation device 10 of the present
embodiment includes the plasma generating electrode 31 of the first
or second invention, the plasma generation device 10 can
simultaneously generate different types of plasma by applying
voltage between the pair of electrodes 35 due to the different
arrangement patterns of the through-holes in the conductive
film(s).
[0073] As shown in FIGS. 11(a) and 11(b), in the plasma generation
device 10 according to the present embodiment, it is preferable
that the plasma generating electrodes 31 each having a pair of
electrodes 35 be disposed in layers inside the casing 11. FIGS.
11(a) and 11(b) illustrate a state in which five plasma generating
electrodes 31 each constituted by a pair of electrodes 5 are
layered for convenience of illustration. However, the number of
plasma generating electrodes 31 to be layered is not limited
thereto. The plasma generating electrode 31 may be configured to
include a plurality of electrodes. Spacers 14 are disposed between
the pair of electrodes 35 constituting the plasma generating
electrode 31 and between the plasma generating electrodes 31 in
order to form a predetermined gap.
[0074] The plasma generation device 10 configured as described
above may be installed in an automotive exhaust system, for
example. In this case, exhaust gas discharged from an engine or the
like is passed through plasma generated between the pair of
electrodes 5 so that toxic substances such as soot and nitrogen
oxide contained in the exhaust gas are reacted and discharged to
the outside as a nonhazardous gas.
[0075] At the time of layering two or more plasma generating
electrodes 31, it is preferable to configure the plasma generation
device 10 so that plasma can also be generated between the layered
plasma generating electrodes 31. Specifically, it is preferable to
configure the plasma generation device 10 so that discharge occurs
not only between the electrode 35a of the electrode 35 constituting
the plasma generating electrode 31a and the electrode 35b disposed
opposite to the electrode 35a, but also between the electrode 35a
of the electrode 35 constituting the plasma generating electrode
31a and the electrode 35b constituting the adjacent plasma
generating electrode 31b, such that plasma can be generated between
the layered plasma generating electrodes 31.
[0076] The plasma generation device of the present embodiment may
include a power source for applying voltage to the plasma
generating electrode (not shown). As the power source, a
conventionally known power source which can supply electricity so
that plasma can effectively be generated may be used.
[0077] The plasma generation device of the present embodiment may
be configured so that current is supplied from an external power
source instead of providing a power source in the plasma generation
device as described above.
[0078] Current supplied to the plasma generating electrode used in
the present embodiment may appropriately be selected depending on
intensity of plasma to be generated. When installing the plasma
generation device in an automotive exhaust system, it is preferable
that current supplied to the plasma generating electrode be a
direct current at a voltage of 1 kV or more, a pulsed current
having a peak voltage of 1 kV or more and a pulse rate per second
of 100 or more (100 Hz or more), an alternating current having a
peak voltage of 1 kV or more and a frequency of 100 Hz or more, or
a current generated by superimposing two of these currents. This
constitution enables efficient generation of plasma.
[0079] Next, one embodiment of an exhaust gas purifying device of
the present invention (fourth invention) is described below in
detail. FIG. 12 is an explanatory view schematically showing an
exhaust gas purifying device of the present embodiment. As shown in
FIG. 12, an exhaust gas purifying device 41 of the present
embodiment includes the plasma generation device 10 of one
embodiment of the third invention and a catalyst 44, the plasma
generation device 10 and the catalyst 44 being provided in an
exhaust system of an internal combustion engine. The plasma
generation device 10 is provided on the exhaust gas generation side
(upstream) of the exhaust system, and the catalyst 44 is provided
on the exhaust side (downstream). The plasma generation device 10
and the catalyst 44 are connected through a pipe 42.
[0080] The exhaust gas purifying device 41 of the present
embodiment is a device which purifies NO.sub.x contained in exhaust
gas under oxygen-rich atmosphere, for example. That is, NO.sub.x is
reformed by plasma generated by the plasma generation device so
that NO.sub.x is easily purified by the downstream catalyst 44, or
a hydrocarbon (HC) or the like in the exhaust gas is reformed so
that HC easily reacts with NO.sub.x, and NO.sub.x is purified by
the catalyst 44.
[0081] The plasma generation device 10 used for the exhaust gas
purifying device 41 of the present embodiment converts NO.sub.x
contained in exhaust gas generated by combustion is oxygen-rich
atmosphere, such as in a lean burn or gasoline direct injection
engine or a diesel engine, into NO.sub.2 by plasma. The plasma
generation device 10 generates active species from HC or the like
contained in exhaust gas. As the plasma generation device 10, a
plasma generation device configured in the same manner as the
plasma generation device 10 shown in FIG. 11(a) may suitably be
used.
[0082] The catalyst 44 is provided downstream of the plasma
generation device 10 in the exhaust system as a catalyst unit 45
provided with a catalytic member including a substrate having pores
through which exhaust gas is circulated are formed. The catalytic
member includes the substrate and a catalyst layer formed to cover
the inner wall surfaces surrounding the pores in the substrate.
[0083] Since the catalyst layer is generally formed by impregnating
the substrate with a catalyst in a slurry form (catalyst slurry) as
described later, the catalyst layer may be called a "washcoat
(layer)".
[0084] The shape of the substrate is not particularly limited
insofar as the substrate has an exhaust gas circulation space. In
the present embodiment, a honeycomb-shaped support having a
plurality of minute holes is used.
[0085] It is preferable that the substrate be formed of a material
exhibiting heat resistance. As examples of such a material, a
porous material (ceramic) such as cordierite, mullite, silicon
carbide (SiC), and silicon nitride (Si.sub.3N.sub.4), a metal (e.g.
stainless steel) and the like can be given.
[0086] The catalyst layer is mainly formed by a porous carrier and
one or more elements selected from Pt, Pd, Rh, Au, Ag, Cu, Fe, Ni,
Ir, and Ga supported on the surface of the porous carrier. Pores
continuous with the pores in the substrate are formed in the
catalyst layer.
[0087] The porous carrier may appropriately be formed of a material
selected from alumina, zeolite, silica, titania, zirconia,
silica-alumina, ceria, and the like. As the catalyst 44, a catalyst
which promotes decomposition of NO.sub.x is used.
[0088] The present invention is described below in more detail by
way of examples. However, the present invention should not be
construed as being limited to the following examples.
EXAMPLE 1
[0089] A plasma generation device having a configuration as shown
in FIG. 11(a) was manufactured. Exhaust gas was treated by using
the plasma generation device, and the amounts of soot, nitrogen
monoxide (NO), and hydrocarbon (HC) contained in the gas after the
treatment were measured, and the presence or absence of aldehyde
was determined. A plasma generating electrode used in the plasma
generation device of this example was manufactured as follows. The
first conductive film having through-holes formed in such an
arrangement pattern that the diameter of the through-holes was 2 mm
and the interval between the adjacent through-holes was 8 mm, and
the second conductive film, having through-holes formed in such an
arrangement pattern that the diameter of the through-holes was 5 mm
and the interval between the adjacent through-holes was 6 mm were
screen-printed on an unfired alumina tape substrate (thickness
after firing: 0.5 mm) by using a tungsten paste to a thickness of
10 .mu.m. At this time, the first conductive film and the second
conductive film were disposed in series on the exhaust gas inlet
side and the exhaust gas outlet side, respectively. After
laminating an alumina tape on the resulting product, the laminate
was fired to form an electrode including a plate-like ceramic body
as a dielectric and the first and second conductive films disposed
inside the ceramic body and having different two kinds of
arrangement patterns. 10 electrodes were formed and layered with 1
mm gap between each electrode so that the electrodes were disposed
opposite to one another to form a plasma generating electrode. The
conductive films constituting each electrode were alternately
connected with power source lines. A pulse power source using an SI
thyristor was connected with one of the power source lines, and the
other power source line was grounded.
[0090] When pulsed current was caused to flow through each
conductive film at a voltage of 5 kV, an energy of 25 mJ per pulse
was supplied to the conductive film having the arrangement pattern
with a diameter of 2 mm and an interval of 8 mm, and an energy of
10 mJ per pulse was supplied to the conductive film having the
arrangement pattern with a diameter of 5 mm and an interval of 6
mm. It is considered that the difference in energy supplied is
caused by the difference in capacitance due to the difference in
the arrangement pattern between the conductive films. A uniform and
excellent discharge state was obtained for both of the conductive
films irrespective of the amount of energy supplied.
[0091] Exhaust gas simulating exhaust gas discharged from an engine
was passed through the plasma generation device. As the exhaust
gas, a gas prepared by mixing 1000 mg/hr of soot into a mixed gas
containing 10 vol % of oxygen, 10 vol % of CO.sub.2, 200 ppm of
propylene, and 200 ppm of NO gas, with the balance being nitrogen,
was used. The concentration of each component contained in the gas
after passing through plasma was measured. The measurement results
are shown in Table 1. TABLE-US-00001 TABLE 1 Comparative
Comparative Example 1 Example 2 Example 3 Example 1 Example 2
Voltage First conductive film 5 5 8 8 4 (kV) Second conductive film
5 5 4 Number of First conductive film 500 100 100 100 1000 pulses
Second conductive film 500 1000 1000 (pulse/sec) Amount of NO (ppm)
60 40 50 120 60 Amount of HC (ppmC) 80 50 60 100 100 Aldehyde
Present Present Present Present Present Amount of PM (mg/hr) 50 60
30 50 900
EXAMPLE 2
[0092] A 5 kV pulsed current was caused to flow through a plasma
generation device configured in the same manner as the plasma
generation device of Example 1 so that the number of pulses applied
to the first conductive film was 100 pulse/sec and the number of
pulses applied to the second conductive film was 1000 pulse/sec.
Measurements were conducted in the same manner as described above.
The measurement results are shown in Table 1.
EXAMPLE 3
[0093] A plasma generation device configured in the same manner as
the plasma generation device of Example 1 was provided. An 8 kV
pulsed current was caused to flow through the first conductive film
so that the number of pulses was 100 pulse/sec, and a 4 kV pulsed
current was caused to flow through the second conductive film so
that the number of pulses was 1000 pulse/sec. Measurements was
conducted in the same manner as described above. The measurement
results are shown in Table 1.
COMPARATIVE EXAMPLE 1
[0094] A pulsed current was caused to flow through a plasma
generation device configured in the same manner as the plasma
generation device of Example 1, except for using an electrode in
which only the first conductive film was formed, at a voltage of 8
kV so that the number of pulses was 100 pulse/sec. Measurement was
conducted in the same manner as described above. The measurement
results are shown in Table 1.
COMPARATIVE EXAMPLE 2
[0095] A pulsed current was caused to flow through a plasma
generation device configured in the same manner as the plasma
generation device of Example 1, except for using an electrode in
which only the second conductive film was formed, at a voltage of 4
kV so that the number of pulses was 1000 pulse/sec. Measurement was
conducted in the same manner as described above. The measurement
results are shown in Table 1.
[0096] As shown in Table 1, in the plasma generation devices of
Examples 1 to 3, soot and NO were effectively oxidized, and
aldehyde, which can improve the performance of the NO.sub.x
reduction catalyst, was produced. The plasma generation device of
Comparative Example 1 and the plasma generation device of
Comparative Example 2 could not effectively treat soot and NO due
to low NO treatment capability and low soot treatment capability,
respectively.
EXAMPLE 4
[0097] An exhaust gas purifying device was manufactured by
disposing a catalyst downstream of the plasma generation device of
Example 1. The NO.sub.x purification-performance of the exhaust gas
purifying device was evaluated. As the catalyst, a catalyst powder
prepared by impregnating commercially-available
.gamma.-Al.sub.2O.sub.3 with 5 mass % of Pt was supported on a
cordierite ceramic honeycomb. The honeycomb catalyst was in the
shape of a cylinder having a diameter of 105.7 mm and a length of
114.3 mm. The number of cells was 400, and the thickness (rib
thickness) of the partition walls partitioning the cells was 4 mil
(about 0.1 mm). The plasma generation conditions and the gas
conditions were the same as those of Example 1.
[0098] As a result, the NO.sub.x concentration was reduced to 110
ppm after the mixed gas having an NO concentration of 200 ppm had
passed through the plasma generation device and the catalyst.
COMPARATIVE EXAMPLE 3
[0099] An exhaust gas purifying device was manufactured by
disposing a catalyst similar to that used in Example 4 downstream
of the plasma generation device of Comparative Example 1. The
NO.sub.x purification performance of the exhaust gas purifying
device was evaluated. The plasma generation conditions and the gas
conditions were the same as those of Comparative Example 1.
[0100] As a result, the NO.sub.x concentration was reduced little
to 170 ppm after NO of 200 ppm had passed through the plasma
generation device and the catalyst.
INDUSTRIAL APPLICABILITY
[0101] Since a plasma generating electrode and a plasma generation
device of the present invention can simultaneously generate
different states of plasma, the plasma generating electrode and the
plasma generation device can suitably be used for a purification
device which purifies exhaust gas containing a plurality of
substances, for example. Since the exhaust gas purifying device of
the present invention includes the above plasma generation device
and a catalyst, the exhaust gas purifying device can suitably be
used as a purifying device which purifies exhaust gas discharged
from an automotive engine or the like.
* * * * *